Every system is composed of some components that interact together in order to achieve a designated target, and an inspection machine is no different. Inspection machines move and take images of wafers. In particular, the imaging process requires a sequence of activities that achieve an imaging of the entire wafer, at the minimum amount of time. The ability to achieve the required purpose, each component should work within given constraints.
As the constraints mount, the complexity of the system will rise. This in turn will increase cost (development, integration and maintenance), and the reliability will be reduced. In contrast, a “loosely bounded” system enables a more cost effective and reliable solution while keeping the end result within the required boundaries.
The Imaging Module
Every AOI system must acquire an image of the wafer for the inspection process. This, of course requires an imaging component which includes a camera (with an appropriate optics), coupled to a light source that can acquire an image. To control the camera, the system requires a frame grabber that will transfer the data to a Computer for later processing.
As the defect resolution seldom permits a single shot for the whole wafer, a motion component is coupled to the imaging component that enables taking images in different locations on the wafer. The Motion Component includes a Motion Device that enables the movement and a Motion controller that activated the Motion device appropriately.
The goal for this Imaging module is to have an image of the whole wafer. As this image is too big to be taken in a single shot, it has to be broken into multiple frames. These frames should:                a. Meet optical requirement.        b. Cover the whole wafer area.        c. Be associated to the right locations on the wafer.        
Continuous Scan
In order to achieve a good performance for the wafer acquisition, the system grabs the image while in movement. That, of course, influences the image quality (smearing). In order to limit the smearing effect, the actual grabbing is done in a short (time) interval. As the user requires a specific position, the traditional sequence is:                a. Camera Shutter opens.        b. Motion controller reaches position (while moving).        c. A short burst of light is generated.        d. Camera Shutter Closes        
This sequence requires a tight coupling between the different components and inherent problems that accompany it. Moreover, as the position is governed by the Motion controller—the speed cannot be accurate and the time between two consecutive images is not accurate. This prevents the system from using the full frame rate of the camera (when the rate exceeds the maximum frame rate—an image will be lost).